Barium bis(dihydrogenorthophosphate)

Melting point / freezing point

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

melting point/freezing point

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04-Dec-2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

GLP guideline study. The performance was without restrictions. However the test results need to be evaluated by comparing other data due to the nature of substancce.

Qualifier:

according to guideline

Guideline:

OECD Guideline 102 (Melting point / Melting Range)

Version / remarks:

adopted July 27, 1995

Qualifier:

according to guideline

Guideline:

EU Method A.1 (Melting / Freezing Temperature)

Version / remarks:

May 31, 2008

GLP compliance:

yes (incl. QA statement)

Remarks:

Hess. Ministerium für Umwelt, Energie, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany

Type of method:

capillary method

Specific details on test material used for the study:

- Appearance: solid/white
- Analytical purity: >92% based on 44.8 % BaO and 42.8 % P2O5
- Batch No.: 9000008613
- Expiration date of the lot/batch: April 23, 2017
- Storage conditions: At room temperature (20 °C ± 5 °C) in the dark

Key result

Melting / freezing pt.:

>= 234.3 - <= 237.3 °C

Atm. press.:

ca. 1 013 hPa

In the preliminary test the test item melted at 245 °C.

The test item showed only two stages of melting. The melting started at 234.3 °C. At 237.3 °C the stage B of melting was reached (for details see Table below). After the stage B the test item was completely liquid.

Results for the Determination of the Melting Point / Melting Range

Experiment No.	Stage A [°C]	Stage B [°C]	Stage C [°C]	Stage D [°C]	Stage E [°C]
1	234.3	237.3	n.d.	n.d	n.d
2	234.3	237.2	n.d	n.d	n.d
3	234.2	237.3	n.d	n.d	n.d
Mean (n=3)	234.3	237.3	n.d	n.d	n.d
	507.4 K	510.4 K	n.d	n.d	n.d

Stage A: Beginning of melting / wet pointStage

B: Shrinkage pointStage

C: Collapse pointStage

D: Liquefying pointStage

E: Final Stage of melting

n.d. not determined

Reference 2

Endpoint:

melting point/freezing point

Type of information:

other: Expert statement based on the experimental tests

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

Differential thermal analysis as well as thermogravimetric analysis were preformed. In addition a sample was determined by XRD at 300 °C to confirm the condensation of orthophosphate to pyrophosphate.

GLP compliance:

no

Type of method:

thermal analysis

Remarks:

as well as themogravimeric analysis

Key result

Atm. press.:

ca. 1 013 hPa

Decomposition:

yes

Decomp. temp.:

>= 240 °C

Based on the company experience of registrant on this type of phosphate substances, the melting point measured for barium bis(dihydrogen orthophosphate) (study no. 108281180) is not really the melting point of substance itself. Because along with increasing temperature the condensation reaction begins, the water is obtained in the test matrix and barium bis(dihydrogen orthophosphate) dissolved in the water at once. Therefore it seems that the substance melts and becomes liquid. However this stage exists only in a short period. When more barium pyrophosphate is formed the substance becomes again an insoluble solid. And during further the polymerization reaction the metaphosphate obtained is more insoluble, and it has a melting point over 1560 °C.

The process of these transitions begins with two phosphate units coming together in a condensation reaction shown as following:

Ba(H₂PO₄)₂    – H₂O    -> BaH₂P₂O₇    – H₂O ->    Ba(PO₃)₂

 

In order to confirm the observation and assumption, the differential thermal analysis as well as thermogravimeric analysis internally. The thermogram shows two mass changes: in the temperature range of 240 – 280 °C and 350 – 400 °C. The first change has a mass loss of 7.02%, which indicates clearly a transition of dihydrogen orthophosphate to pyrophosphate (BaH2P2O7). Afterwards barium pyrophosphate polymerizes sequently to metaphosphate [Ba(PO3)2] at 350 – 400 °C with a mass loss of 3.60%.

Also the registrant has characterized the substance at 300 °C by means of X-Ray powder diffraction. Comparing with the standard diffractogram of barium bis(dihydrogen orthophosphate), barium pyrophosphate and barium metaphosphate, it shows that the test substance changes completely at 300 °C and condenses to barium pyrophosphate or barium metaphosphate.

Therefore it can be concluded that the substance barium bis(dihydrogen orthophosphate) decomposes before melting and boiling. The condensation reaction followed by polymerization happens along with increasing temperature.

Description of key information

not applicable

Additional information

The test substance decomposes before melting and boiling. The condensation reaction followed by polymerization happens along with increasing temperature (DTA and TGA). The substance becomes barium pyrophosphate or barium metaphosphate, which are confirmed by XRD.